1. Field of the Invention
The present invention relates to a contactless ignition system for internal combustion engines or more in particular to a contactless ignition system for internal combustion engines which is controlled electronically in accordance with the engine operating conditions including the engine intake negative pressure, intake temperature and throttle opening.
2. Description of the Prior Art
An example of the electronic advancing system for automatically advancing ignition timing in accordance with the engine r.p.m. of an internal combustion engine is disclosed in U.S. Pat. No. 3,885,534 assigned to Webster on May 27, 1975. In this advancing system, during the rotation of the crank of the internal combustion engine by 4.pi./c (c: number of cylinders), the input signal is integrated, and when this integrated output coincides with a reference value, an ignition signal is generated. The ignition timing is determined by adjusting the reference value. When the reference value is reduced, for instance, the timing of coincidence between the integrated output and the reference value is advanced, thus advancing the ignition timing.
In the above-mentioned system, the integrated output is always required to correspond to the rotational angle of the crank shaft. In the case where a predetermined input signal is applied to an integrator having a predetermined integration constant, the integration time is shortened with the increase in r.p.m. so that the integrated output is reduced for the same rotational angle of the crank shaft, thus failing to correspond to the rotational angle of the crank shaft. The system disclosed in the U.S. Pat. No. 3,885,534 comprises a feedback system for controlling the input signal to the integrator in accordance with the engine rotational speed thereby to attain coincidence between the integrated output and the rotational angle of the crank shaft. This complicates the system.
According to the U.S. Pat. No. 3,939,811 assigned to Sasayama on Feb. 24, 1976, on the other hand, a capacitor is charged by a constant current during the rotation of the crank shaft by a predetermined angle, followed by discharge of the capacitor by a constant current, and when the capacitor voltage reaches a predetermined level, an ignition signal is generated. In this case, the charge and discharge time of the capacitor is not related to the rotational speed of the crank shaft, thus leading to the advantage that the integrated output always coincides with the rotational angle of the crank shaft without any feedback system.
In the case of an internal combustion engine, especially, an internal combustion engine for the motor bicycles, it is generally required that the advance angle of ignition timing be controlled in accordance with the intake negative pressure, intake air temperature and throttle opening. In the aforementioned system, the width of the advance angle cannot be controlled.